The present invention relates to a new and improved 4-quadrant drive device of high precision.
Generally speaking, the 4-quadrant drive device of high precision of the present invention contains two motors which act by means of a respective gearing upon a load movable about an axis in both rotational directions, and the excitation currents of which are controlled by adjustment or setting elements. The motors operate at least partially in counteracting fashion with small summation drive torques in order to eliminate the gearing backlash or play, however these motors act in the same direction in the presence of large summation drive torques.
In drive systems the backlash or play between the motor and the load leads to instabilities and inaccuracies if disturbances act upon the load. Therefore, for high precision drives measures must be undertaken in order to eliminate the aforementioned backlash or play.
Thus, in German Pat. No. 1,290,232, published Mar. 6, 1969, there has been disclosed a drive device containing two direct-current shunt motors which counteract one another with the same torque at standstill. During an accceleration in the rotational direction of the one motor the armature current of this motor is increased and at the same time there is attenuated the field of the other motor. With a drive device of this type only one of the two motors can be effectively employed during acceleration, whereas the other motor acts in the opposite sense for exerting a counteracting effect. The small drive output and the energy losses constitute appreciable drawbacks of a drive device of this type.
Furthermore, there is known to the art a drive system containing two parallely connected electric motors having double-series excitation and external excitation. Such electric motors are provided with two circular current-free 4-quadrant power adjustment elements possessing individual current regulation, an adjustment element with current regulation for the external excitation as well as an analog electronic control for the realisation of the desired current-torque characteristic. Such type of drive system enables both of the motors to act in the same direction with large summation drive torques. In this way there can be improved the drive output, however there is required a considerable expenditure in power electronic means, which is particularly necessitated due to the installation of two complete 4-quadrant power adjustment elements.